Tower cranes

ABSTRACT

The invention relates to a tower crane. This crane includes a crab-jib rigidly united with a slewing upper tower section and a counterweight-jib hingedly connected to said section, each of these jibs being connected by at least one tie to a post hingedly connected to the slewing section, the attachment points of the ties on the post lying at a level higher than that of the jibs. The invention makes it possible to dispense with a tower head and thus reduces the total crane area offered to the wind. It further enables the jibes to be less heavily dimensioned.

United States Patent 1191 Durand Dec. 3, 1974 1 [75] Inventor:

' Related U.S. Application Data [63] Continuation ofS er. No 1'T i,"869TFeb. 12, 1971,

abandoned.

[30] Foreign Application Priority 1H1? [58] Field of Search 212/46 R, 46 A, 46 B, 47,

FOREIGN PATENTS OR APPLICATIONS 1,413,966 9/1965 France 212/48 Primary Examiner-James B. Marbert Assistant Examiner-James L. Rowland Attorney, Agent, or FirmWatson, Cole, Grindle & Watson I 5 7 1 ABSTRACT The invention relates to a tower crane. This crane includes a crab-jib rigidly united with a slewing upper tower section and a counterweight-jib hingedly connected to said section, each of these jibs being connected by at least one tie to a post hingedly connected to the slewing section, the attachment points of the ties on the post lying at a level higher than that of the jibs. The invention makes it possible to dispense with a tower head and thus reduces the total crane area offered to the wind. It further enables the jibes to be less [56] References cued heavily dimensioned.

UNITED STATES PATENTS 2,413,701 1/1947 Faure et al 212 49 3 Claims, 7 Drawing Flgllres 3,706,285 12/1972 Gynt er al....' 212/144 x F/G.:-7 I A filed Feb. 12, 197 l abandoned.

The province of this invention is that of tower cranes.

Prior art tower cranes include those comprising a lower tower section fixed on a platform or base, an upper tower section capable of slewing on the lower section, a tower head fixed onto the upper section, a jib hinged to the base of the tower head and supporting a load-bearing crab capable of travelling along its length, and a jib hinged to the base of the tower head and supporting a counterweight capable of travelling along its length, the jib supporting the crab and the jib supporting the counterweight being hinged to opposite sides of the tower head and being each held horizontal by a tie of constant length having its ends fixed to the jib and to the top of the tower head respectively.

In this type of crane the counterweight-jib tie has to withstand, under duty conditions and for a given position of the counterweight, a permanent load due to the dead weight of the counterweight-jib and the weight of the counterweight. Further, the crab-jib tie is subjected to a load which varies between two positive values:

a minimum'value .due to the dead weight of the crabjib;

and a maximum value resulting from the dead weight of the crab-jib and the maximum moment exerted by the burden to be lifted.

In order to ensure minimum absolute loads appliedsto the tower head, the weight of the counterweight is usually calculated so that the sum of the moments generated by the dead weight of the counterweight-jib and the weight of the counterweight, with respect to the vertical axis of the tower head, balances the moments, with respect to that axis, generated by the dead weight of the crab-jib and by one half the burden to be lifted that will produce the maximum permissible moment.

The tower head is accordingly subjected to a moment M which varies between two values of opposite sign. In

other words; s. Ina.ximum moment clue to the burden +maximum moment due to the burden Thus the tower head is subjected to alternating bending loads. In this type of crane, the need to have a tower head to restrain the two horizontal jibs by means of ties anchored to it adversely affects crane stability, especially that of tall cranes, owing to the surface which the tower head offers to the wind.

Since the jibs on cranes of the kind mentioned above have fixed positions in relation to the tower head, it is in theory unnecessary to provide a hinged connection between the tower head and each jib. Certain crane builders have consequently designed the jibs to be rigidly mounted on the slewing portion of the tower, thereby dispensing with the tower head and the two ties. With this type of crane the jibs are rigidly embedded, as it were, in the slewing portion of the tower.

In this type of design, because there are no ties, all

the bending moments to which the jibs are subjected-v are transmitted to the crane tower through each restrained jib foot. The foot of the counterweight-jib must'be able to transmit the bending moments due to.

the dead weight of the counterweight-jib and to the able to transmit the bending moments due to the dead weight of the crab-jib and to the burden to be hoisted.

This leads to oversizing the jibs, particularly in the region of the jib feet, and to a consequent increase in weight and cost.

The present invention relates to new cranes free of a tower head, the jibs of which are nevertheless of reasonable size.

A crane according to this invention, which comprises a lower tower section, an upper tower section capable of slewing on the lower tower section, a crab-jib and a counterweight-jib, is characterized in that the crab-jib is rigidly fixed to the slewing upper tower section and the counterweight-jib is hingedly connected to the slewing tower section on the side thereof remote from the crab-jib, the crab-jib and the counterweight-jib being each connected by at least one tie to a post the lower end of which, is hinged onto the slewing tower section or onto that end of the crab-jib which overlies. said slewing tower section, the tie attachment points on the post lying at a level higher than that of the jibs.

Cranes according to this invention are free of tower heads, resulting in an appreciable saving in weight and decrease in area offered to the wind. Further, by reason of the provision of ties, cranes according to this invention require no oversizing of the jibs. Further the subject cranes of the present invention, although they comprise an embedded jib and ties, remain isostatic,

thereby facilitating their design.

A crane according to this invention may comprise a tie interconnecting the upper end of the post with a point on the crab-jib, or a plurality of ties interconnecting said upper end with a plurality of different points on the jib.

The description which follows with reference to the accompanying non-limitative exemplary drawing will give a clear understanding of how the invention can be carries into practice.

In the drawing:

FIG. 1 is a schematic side elevation view of the upper part of a crane according to this invention, having a single tie connecting the post to the crab-jib;

FIG. 2 is a schematic side elevation view of the upper part of a crane according to the invention, comprising two ties connecting the post of the crab-jib;

FIG. 3 is a fragmental diagrammatic showing of the boxed-in portion of FIG. 2, illustrating an alternative embodiment;

FIG. 4 is a schematic fragmental side elevation view of a crane according to the invention, comprising more than two ties for connecting the post-to the crab-jib;

FIG. 5 is a fragmental schematic side elevation view of a further crane according to the invention, comprising more than two ties for connecting the post to the crab-jib;

FIG. 6 is a schematic side elevation view of the upper part of an alternative embodiment of a crane according to this invention; and

FIG. 7 is a schematic side elevation view of the upper part of still another alternative embodiment of a crane counterweight itself. The foot of the crab-jib must be according to this invention.

Reference is first had to FIG. 1 for a showing of a crane according to this invention. This crane includes a lower tower section 1 which isfixed, for instance, to a platform (not shown); an upper tower section 2 mounted at 2a for slewing motion upon section 1 and of the post with a point 13 on the crab-jib; and a tie 14 interconnecting the top 12 of the post with the outer end 15 of counterweight-jib 6. The burden-hoisting crab and the counterweight 7 are capable of travelling along their respective jibs as required. Alternatively, the hinge points 8 and 10 may be made one and the same. Similarly, the ties l1 and 14 could be fixed to the post at different points thereon.

For a given value and position of counterweight 7, the force F in tie 11 remains constant. As in the case of the prior art tower-head cranes referred to precedingly, the value of counterweight 7 is preferably determined so that tower section 2 is subjected to optimum bending conditions, that is to say so that it is subjected to au m Mx qbstwsena-..

maximum moment due to the burden 2 and +maximum moment due to the burden Under duty conditions, since the relieving force-F exerted by tie 11 is constant irrespective of the burden C carried by crab 5, the jib 4 may be likened to a restrained beam subjected to a constant known force F directed from the point 13 to the point 12, andto a downwardly directed force C (the weight of the burden) the value and point of application of which on jib 4 both vary.

It may be seen that, in the case of a crane according to this invention, not only does the counterweight balance the moments loading the crane tower, but it also relieves the stresses in the crab-jib because of the action of swinging post 9, whereas in conventional cranes the counterweight has no effect on the crab-jib and its only purpose is to balance the moments exerted at the vertical axis of the crane tower by the burden and the crab-jib.

Thus, in a crane according to this invention, the foot of the restrained crab-jib can be loaded only:

by an upwardly directed bending moment M, under no-load conditions, and

by a downwardly directed bending moment +M, under full-load conditions, M being equal to one half the maximum moment due to the burden.

The latter moment +M is far smaller than the moment sustained by the crab-jib of cranes with restrained jibs and'devoid of ties, such moment being equal, to the maximum moment due to the burden (+2M) plus the moment due to the weight of the crab-jib.

The present invention thus permits a much more modestly sized crab-jib, yet retains the advantage of dispensing with the tower head.

Reference is next had to FIG. 2 for an alternative embodiment of a crane according to this invention, in which the post 9 is hinged onto the slewing tower section at 10', and comprising two ties interconnecting the post with the crab-jib.

These two ties 20 and 21 are formed by a single steel rope which has its ends fixed to two points 22 and 23 on the crab-jib and which runs over a pulley 24 pivotally attached to post 9, whereby the force F is automatically distributed between the two ties. Alternatively, as

shown in FIG. 3, the rope and pulley of FIG. 2 may be replaced by a bcam-lcvcr 30 fulcrumed at 3l on the post 9 and having the ends 32 and 33 of its arms attached to ties 34 and 35 which have their other ends I fixed to different points on the crab-jib.

Reference to FIG. 4 shows another alternative embodiment of a craneaccording to the invention, comprising four ties interconnecting the post with the crabjib.

These four ties 40, 41a, 41b and 42 are formed by a steel rope which has its ends fixed to two points 43 and 44 on thecrab-jib and which runs in succession, start- I ing from attachment point 43,over a pulley 45 pivotally attached to post 9, over a pulley 46 carried on the crab-jib at a point intermediate points 43 and 44, and thereafter over a pulley 47 mounted in parallel with pulley 45, before being attached to the point 44. As with the embodiment of FIG. 2, the force F is automatically distributed among the several ties.

Referring now to FIG. 5, the embodiment of a crane according to the invention shown thereon comprises three ties interconnecting the post with the crab-jib.

These three ties 50, 51 and 52 rspectively have one of their ends attached to points 53, 54 and 55 on the crab-jib. Ties 50 and 51 each havetheir other end attached to the ends 56, 57 of a beam-lever 58 fulcrumed on one end 59 of a beam-lever 60 the other end 61 of which is attached to tie 52, the beam-lever 60 being in turn fulcrumed to post 9. Here again the force F is automatically distributed among the ties.

By reason of the provision of several ties interconnecting the crab-jib with the post in the embodiments illustrated in FIGS. 2 through 5, his possible to use a crab-jib of lighter construction than in the embodiment of FIG. 1.

In the case of the cranes illustrated in FIGS. 1 through 5, it is possible, when telescoping or erecting the crane, to obtain a substantially zero resultant moment with respect to the vertical crane axis, since the toppling moment can be balanced by appropriately adjusting the position of the counterweight along the counterweight-jib.

FIGS. 6 and 7 portray crane embodiments according to this invention-comprising a counterweight-jib which is simplified in that the counterweight is fixedly located in relation to its jib. In such embodiments, balancing during crane telescoping or erection is achieved by a luffing motion of the counterweight-jib.

More specifically, FIG. 6 depicts a crane comprising a counterweight-jib consisting of a single beam supporting a fixed counterweight 71 on its end remote from its hinge point 8. The counterweight-jib is connected to post 9 by a tie 14 and crab-jib 4 is connected to post 9 by a tie 72 of variable length. Tie 72 is formed by a steel rope which has one end fixed to post 9 and which runs over a pulley 73 carried on the crab-jib and thereafter winds around a winch 74. The length of tie 72 can be varied very simply by operating winch 74.

The dash lines in the figure illustrate an intermediate raised position of the counterweight jib. As will readily be appreciated, the resultant moment M with respect to the vertical rotation axis of the crane, due to the weight of the counterweight-jib and the weight of the counterweight itself, gradually decreases as the counterweight-jib is swung upwards from its horizontal position corresponding to the maximum value of the moment M.

Reference is lastly had to FIG. 7 for still another embodiment permitting luffing motion of the counterweight-jib. In this embodiment the ties 80 and 81 interconnecting the post with the jibs are of fixed length. Luffing motion of the jib is accomplished by exerting a pull on the points 82 and 83 of the ties by means of a system which can be actuated by the burdencarrying crab 5 of the crab-jib, as shown, or alternatively by means of an independent winch. This system includes a steel rope 84 which has one of its ends attached to crab 5 and thereafter runs in succession over a first pulley 85 carried by tower section 2, over a second pulley 86 hingedly connected to the point 82 on the tie 81 interconnecting post 9 with the counterweight-jib, over a third pulley 87 mounted in parallel with pulley 85, and over a fourth pulley 88 hingedly connected to the point 83 on the tie 80 interconnecting post 9 with the crab-jib, before it is ultimately attached to a fixed point 89.

It will be manifest that in this arrangement all that is necessary is to cause crab 5 to travel in the direction of the outer end of the crab-jib for a pulling force to be exerted on the tie points 82 and 83 that will tend to impart luffing motion to the counterweight-jib and swing the post 9 about its hinge point 10 in a counterclockwise direction. An intermediate raised position of the counterweight-jib is shown in dash lines.

It goes without saying that changes and substitutions may be made in the specific embodiments described hereinabove without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. A tower crane, comprising:

a lower tower section and an upper towersection;

a jib supporting a burden-carrying crab movable along the length thereof, said jib is connected with the top part of said upper tower section so as to form therewith a rigid unit;

a counterweight-jib;

means for pivotally connecting said counterweightjib to said rigid unit on the side thereof remote from said crab-jib;

a post erected on said rigid unit to project above the same;

tie members attached to the upper end of said post for connecting said end to said crab-jib and to said counterweight-jib respectively; and

means for pivotally connecting the lower end of said post to said rigid unit so as to permit said post to swing fully under the action of the forces exerted on it by said tie members. 7

2. A tower crane as in claim 1, further comprising means at the lower part of said upper tower section for allowing a slewing motion thereof on said lower tower section.

3. A tower crane as in claim 1 wherein said crab-jib overlies the slewing tower section. 

1. A tower crane, comprising: a lower tower section and an upper tower section; a jib supporting a burden-carrying crab movable along the length thereof, said jib is connEcted with the top part of said upper tower section so as to form therewith a rigid unit; a counterweight-jib; means for pivotally connecting said counterweight-jib to said rigid unit on the side thereof remote from said crab-jib; a post erected on said rigid unit to project above the same; tie members attached to the upper end of said post for connecting said end to said crab-jib and to said counterweightjib respectively; and means for pivotally connecting the lower end of said post to said rigid unit so as to permit said post to swing fully under the action of the forces exerted on it by said tie members.
 2. A tower crane as in claim 1, further comprising means at the lower part of said upper tower section for allowing a slewing motion thereof on said lower tower section.
 3. A tower crane as in claim 1 wherein said crab-jib overlies the slewing tower section. 